Our previous research efforts indicate that chronic schrizophrenic subjects, other chronic mental patients, and normal controls can be differentiated by examining selected aspects of the electroencephalographic field, with the assistance of computer analysis. The ongoing EEG, and the EEG related to a non-significant auditory stimulus are investigated under different conditions and using varying analytic techniques. Delta-band power, as indicated by the power density spectrum, is utilized as one measure to equate levels of arousal. Findings to date indicate that the chronic schizophrenic subjects may be differentiated by EEG spectral characteristics, the variability of these characteristics, and the auditory evoked changes in electric field pattern. The latter appears to be the most sensitive differentiator, as indicated by the averaged evoked vector electroencephalogram from the central region of the head. Experimental manipulation of acute arousal indicates that the EEG changes caused by this are not similar to those seen in patients. Further studies of chronic arousal are proposed. Experimental procedures are proposed to clarify whether the source of excess beta band power in the chronic schizophrenic results from electromyographic contamination. Cross-spectral coherence studies and the character of the cumulative distribution function are being utilized to help evaluate the question of local and regional cerebral organization and responsiveness to stimulation. The various electroencephalographic measures are being related to patient clinical parameters in an effort to clarify or delineate nosologic entities. Psychotropic medication and severity of illness appear to affect some EEG parameters. Intra-, as well as inter-subject variation related to chemical and medicative status is being studied. The design utilizes hypothesis-forming and hypothesis-confirming subject groups.